Production of acrylic acid by two-stage gas-phase catalytic oxidation of propylene has been widely practiced on industrial scale. This reaction consists of the first stage reaction for gas-phase catalytic oxidation of propylene to acrolein and the second stage reaction for gas-phase catalytic oxidation of the acrolein to acrylic acid.
Heretofore proposed methods for practicing the reaction can be broadly classified into two, i.e., those using two reactors and those using a single reactor.
As one of the methods using two reactors, for example, JP Sho 53(1978)-15314A and JP Sho 55(1980)-102536A (corres. to U.S. Pat. No. 4,365,087) disclose a method using two reactors of the first stage reactor filled with a first stage catalyst suitable for the first stage reaction and the second stage reactor filled with a second stage catalyst suitable for the second stage reaction, and comprising introducing the reaction gas containing mainly acrolein as discharged from the first stage reactor, together with recycle gas, oxygen, or inert gas such as nitrogen or steam into the second stage reactor, and further oxidizing the acrolein to produce acrylic acid.
On the other hand, as one of the methods for producing acrylic acid from propylene using a single reactor, for example, JP Sho 54(1979)-19479A (corres. to U.S. Pat. No. 4,203,906), JP Sho 54(1979)-21966A (corres. to U.S. Pat. No. 4,203,906) and JP Hei 11(1999)-130722A (corres. to U.S. Pat. No. 6,069,271) disclose a method for producing acrylic acid from propylene using a single reactor whose shell space is divided into two reaction zones with a partition plate, which is so designed that a heat transfer medium can be circulated at the shell space of each of the reaction zones independently of each other, the reaction tubes in one of the reaction zones being filled with a first stage catalyst suitable for the first stage reaction and the reaction tubes in the other reaction zone being filled with a second stage catalyst suitable for the second stage reaction.
JP 2001-137689A (corres. to U.S. Pat. No. 6,808,689) discloses a technique to enhance the elimination efficiency of the heat generated in the oxidation reaction by a heat transfer medium, by means of baffle plates or the like which are mounted inside of each shell to regulate the flow of the heating medium.
Also JP Hei 7(1995)-73674B (corres. U.S. Pat. No. 5,048,601) discloses a technique of fixing a partition plate or plates on inner wall of the shell, through a cylindrical fixing plate.